The present disclosure relates to a positive electrode and a nonaqueous electrolyte battery, and particularly relates to a positive electrode and a nonaqueous electrolyte battery, which are capable of suppressing gas generation and the battery swelling that accompanies it.
In recent years, with the spread of portable devices such as video cameras and laptop personal computers, there is an increasing need for small-size, high-capacity secondary batteries. As secondary batteries, nickel-cadmium batteries and nickel-hydrogen batteries using an alkali electrolytic solution are currently used. However, their battery voltages are as low as about 1.2 V, and it is difficult to improve energy density. For this reason, studies have been made on lithium metal secondary batteries using lithium metal. Lithium metal has a specific gravity of 0.534, the lowest among solid elementary substances, and also has an extremely low potential. Further, its current capacity per unit weight is the highest among metal negative electrode materials.
However, in a secondary battery using lithium metal for the negative electrode, dendritic lithium (dendrite) deposits on the surface of the negative electrode at the time of charging, and it grows through charge/discharge cycles. The growth of dendrites not only degrades the charge/discharge cycle characteristics of the secondary battery. In the worst case, they break through the barrier (separator) disposed to prevent contact between the positive electrode and the negative electrode. As a result, an internal short circuit occurs, causing thermal runaway, whereby the battery is broken.
Therefore, as described in JP-A-62-90863, for example, a secondary battery using coke or a like carbonaceous material for the negative electrode, in which charging and discharging are repeated by doping with alkali metal ions and de-doping, has been proposed. This has been proven to solve the problem of degradation of the negative electrode during repeated charging and discharging mentioned above.
Meanwhile, as a result of the search for and development of high-potential active materials for use as positive electrode active materials, materials with a battery voltage of about 4 V have emerged and are attracting attention. Known examples of such active materials are inorganic compounds, such as alkali-metal-containing transition metal oxides and transition metal chalcogens.
Among these, a lithium transition metal composite oxide containing nickel or cobalt as a main component, such as LixNiO2 (0<x≦1.0) or LixCoO2 (0<x≦1.0), holds the greatest promise for high potential, stability, and long life. In particular, a lithium transition metal composite oxide containing nickel as a main component is a positive electrode active material having relatively high potential. The use of such a positive electrode active material for a battery is expected to achieve high charging current capacity and improve energy density.